Brazil’s president Dilma Rousseff has begun the fight for her political life after the first impeachment proceedings for more than 20 years were launched against her in Congress.

Death by 1,000 defamations: Brazil riven by slow-burn impeachment struggle

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After months of jockeying, the removal proceedings were pushed forward by her political nemesis – the lower house speaker Eduardo Cunha – as Brazil slipped deeper into a crisis that has hamstrung decision-making even while the economy suffers its worst downturn since the Great Depression.

On Wednesday night, Cunha finally gave the green light to an opposition motion for the country’s first female president to be ejected from office on allegations that she broke fiscal laws by window dressing government accounts ahead of her re-election last year.

Rousseff came out fighting. “I have received with indignation the decision by the head of the lower chamber to [launch] the impeachment process,” she said. “There is no wrongful act committed by me, nor are there any suspicions that I have misused public money.”

In a televised address to the nation, Rousseff expressed her “outrage” at Cunha’s decision and said there was no evidence of any wrongdoing by her.

“I’ve committed no illicit act, there is no suspicion hanging over me of any misuse of public money,” the president said. “I don’t have any offshore bank accounts, I have no hidden assets.” Her comment was a direct jab at Cunha, who has been charged with taking millions in bribes in connection to a kickbacks scheme that has embroiled state-run oil company Petrobras.

Activists from the ruling Workers Party accuse Cunha and his supporters of plotting a coup.

Earlier this year, Cunha acknowledged that an impeachment, which would be the first since 1992, would be a “backwards step for democracy”. For months, he has sat on more than half a dozen previous opposition proposals to remove an elected head of state who has served only one year of her four-year mandate.

However, he has changed his tone as his own position has come under threat. Julius Camargo, one of the whistleblowers in the Lava Jato investigation into corruption at Petrobras, has testified that the Cunha asked him for a $5m bribe – a claim that the speaker denies.

As pressure on Cunha mounted on Wednesday, he finally accepted a case lodged by opposition lawyers Hélio Bicudo, Miguel Reale and Janaína Paschoal.

It appeared at least partly motivated by self-defence, coming just hours after lawmakers the Workers Party ethics committee announced plans to seek his dismissal on grounds of corruption.

Cunha dismissed the idea that his decision was motivated by personal or political reasons. “The basis of this [impeachment proceeding] is purely technical,” he claimed.

On his Facebook page, he wrote that he was responding to the demands of anti-government protests earlier this year. “The demonstrations that took place throughout Brazil – on March 15, April 12 and August 16 – were not in vain!” he wrote. “The [impeachment] process will be followed by the entire population.”

To proceed, the removal proposal needs the support of at least two-thirds of the deputies, or 342 of the 513 votes in the lower house.

If that is successful, Rousseff will have to hand over power to vice-president, Michel Temer – who is from the same Democratic Movement party (PMDB) as Cunha – for several months while an inquiry is conducted by the senate. A final decision would then have to be approved by a two-thirds majority in the upper house.

Rousseff, who won a narrow but uncontested mandate, may have the votes needed to remain in power, but the escalation of conflict between two of the country’s most powerful figures looks set to worsen the already gloomy outlook for Brazil.

Luciano Dias, a political consultant at the Brasilia-based Analise Politica firm, said: “The chances of President Rousseff being impeached aren’t as big as politicians say now, despite this bold move by Cunha.”

“They are not insignificant, but they are not huge.”

The impeachment debate adds to an already long list of problems for the president: the worst scandal in the country’s history, popularity ratings that have slumped into single digits and a worsening recession.

The latest economic figures this week showed Brazil is now heading for its worst downturn since the Great Depression of the 1930s.

Unemployment is at a five-year high, inflation is nearly twice the government’s target, the value of wages has fallen about 5% since May 2014, and the nation’s GDP is forecast to shrink this year by about 4%.